Cerebral aneurysms affect a substantial fraction of the adult population and are increasingly detected with noninvasive imaging. Only a small fraction of aneurysms rupture, but subarachnoid hemorrhage secondary to aneurysm rupture is a devastating event that carries high rates of morbidity and mortality, and large healthcare costs. Although improving, endovascular and surgical interventions still carry significant risks that may exceed the natural rupture risk. Therefore, it is important to properly evaluate aneurysms to avoid unnecessary interventions of low risk aneurysms, and to identify high-risk aneurysms for immediate treatment. The most important predictors of aneurysm rupture according to past studies are size and location. However, it is well known that many small aneurysms do rupture. On the other hand, the posterior communicating artery (PCOM) is a common site for intracranial aneurysms and aneurysms at this location have larger risks than those at other locations. As such, clinicians often need to decide whether or not to treat PCOM aneurysms, but do not have other reliable parameters to guide and support their decisions. PCOM aneurysms have different angio- architectures (relationship of the aneurysm with respect to the parent artery). However, it is unknown whether aneurysms with different angio-architectures have different rupture rate. Our preliminary data suggests that they do. But, it remains unknown if ruptured or unruptured PCOM aneurysms with different angio-architectures have different hemodynamic and geometric features that explain the different rupture rate and distinguish vulnerable from benign aneurysms. The objectives of this project are to: 1) statistically confirm that PCOM aneurysms with different angio-architectural configurations have different rupture rates, 2) identify hemodynamic and geometric parameters that distinguish between ruptured and unruptured aneurysms of each architecture, and 3) provide clinicians with another tool in the armamentarium to face the neurovascular pathology, by developing a scoring scale for the rupture risk assessment of PCOM aneurysms. Clinical relevance of the proposed project: The results of this exploratory project will be applicable immediately to the clinical practice, and will be generalized and extended in future studies to other locations and aneurysm characteristics. Successful completion of this project will: 1) provide new knowledge to distinguish between vulnerable and benign PCOM aneurysms, 2) improve safety and outcome of aneurysm treatment by better patient selection, 3) advance our understanding of mechanisms responsible for aneurysm rupture, 4) guide future experiments and research, 5) guide development of procedures and devices. Each of these factors will contribute to the improvement of patient care.